Set aside what you think of guns or immigration as a matter of public policy or even morality. Instead, think of them as dye markers of how our cultural politics and the nature of the two parties have changed over time.

In the 1990s, it was common for Democrats to fret over both illegal and legal immigration. "All Americans," President Clinton said in his 1995 State of the Union address, "are rightly disturbed by the large numbers of illegal aliens entering our country."

Barbara Jordan, the civil rights icon and onetime Democratic congresswoman, headed a commission which concluded that legal immigration rates should be modestly cut.

Meanwhile, countless Republicans championed immigration. "I'm hard-pressed to think of a single problem that would be solved by shutting off the supply of willing and eager new Americans," then-House Majority Leader Dick Armey said in 1995. "If anything ... we should be thinking about increasing legal immigration."

After a 1995 meeting with the National Restaurant Association, newly elected House Speaker Newt Gingrich said, "I think we would be a very, very self-destructive country if we sent negative signals on legal immigration."

Back then, boosting legal immigration was seen by many on the left as a sop to big business. The ruling industrial class allegedly wanted a reserve army of cheap labor. As recently as 2015, avowed socialist Sen. Bernie Sanders sounded downright Bannonesque in telling Vox.com that "open borders" was a "Koch brothers proposal ... a right-wing proposal, which says essentially there is no United States."

Sanders is an intriguing example of how political and cultural currents swirl around us. He won his first bid for Congress in 1990 in part because he received the full-throated endorsement of the National Rifle Association. Sanders, the former mayor of Burlington, Vermont, was noncommittal on an assault-weapons ban while his GOP opponent, Peter Smith, flip-flopped and came out in favor of a ban.

"It is not about Peter Smith vs. Bernie Sanders," the NRA's Wayne LaPierre explained. "It is about integrity in politics."

This history was just one reason why it was amusing to listen to LaPierre at the Conservative Political Action Conference last week railing against the "socialists" determined to grab everyone's guns. The man who helped launch the most prominent American socialist since Norman Thomas suddenly thinks socialism is an existential threat to liberty.

What's going on?

On the immigration front: Democrats are increasingly invested in permissive policies in large part because they've bought into the theory that diverse populations are their key to electoral victories going forward. In dialectic fashion, Republicans are increasingly invested in restrictive policies in large part because they're chasing after ever-larger segments of the white vote.

As for firearms: Democrats passed an assault-weapons ban in September 1994. Even Bill Clinton credited that decision as one of the chief reasons the GOP took back the House two months later.

True or not, the more important consequence was that gun rights increasingly became a partisan issue, and the NRA had little choice but to become an adjunct of the GOP. The dynamic became centrifugal, with Democrats and Republicans becoming ever more defined by the issue.

All of these changes were driven by facts on the ground. To listen to Democrats, Republicans support gun rights because the NRA tells them to. In reality, Republicans support gun rights because their voters tell them to, just as Democratic voters tell their representatives the opposite.

But guns and immigration are not simply drivers of polarization, they are examples of its power. Politics has become a lifestyle, part of the "Big Sort" driving so much in our culture. That's why the NRA's marketing these days has so little to do with gun policy and so much to do with smash-mouth cultural resentments.

These days, if you're a Democrat, you're likely to be a down-the-line Democrat on a host of unrelated issues. Same if you're a Republican. Like our representatives, many of us won't buck party orthodoxy on any matter of importance.

Liberals such as Sanders have talked about "two Americas" for generations, but they worked on the assumption that this divide was class-based. It's not. It's cultural, and the divide is becoming a chasm.